In the past bottom hole assemblies (BHAs) have been used that included a pilot bit and a reamer. The drill string to which they were attached extended through a liner so that when a troublesome zone was encountered the liner could be used to isolate it. In the course of drilling, the pilot bit or the reamer could wear out or otherwise require removal from the wellbore; for example, to change the type of bit employed. Pulling the BHA through the liner to change the pilot bit for example would not normally be a problem when using a reamer with extendable arms. This was true as long as the arms retracted when needed so the BHA could be pulled out with the liner supported with slips on the rig floor. However, one problem with the extending arm reamers was that the arms could malfunction and refuse to retract. This would in turn prevent the BHA from coming out through the liner and would require pulling the whole liner out of the hole. This would take a great deal of time and result in extra costs.
Another approach that was tried before was to drive the reamer bit from the BHA with splined surfaces but to support the reamer bit off the bottom of the liner with a bearing. Thus the weight of the reamer bit was carried by the liner while a spline on the BHA transmitted torque to the reamer bit. The idea was that when the pilot bit had to be changed the BHA could simply be pulled through the liner and the splines would release leaving the reamer bit attached at the bottom of the liner. When the pilot bit was renewed, the BHA would be advanced back through the liner and the splines of the BHA would again engage the reamer bit and more hole could be made with weight set on the pilot bit and the liner, possibly with the use of a thruster to maintain even weight on bit. The problem with this design was that the bearing on the lower end of the liner was large and prone to failure before the entire hole was made. If that happened, the liner would have to come out to replace the bearing. This, again, consumed a lot of time and increased costs. An additional limitation was that such a design required that the reamer bit remain near the liner bottom and did not allow for reaming proximate the pilot bit in the event the pilot bit was required to be operated at a distance downhole from the liner bottom.
What is needed and provided by the present invention is a way to temporarily latch the reamer bit to the liner as the BHA is removed so that when the BHA is reinserted it can reliably engage the reamer bit while releasing it from its temporary support position on the liner, and to allow the reamer bit to be latched to the BHA during drilling and/or BHA removal to provide for latching of the reamer bit with the latch profile on the liner bottom. These and other advantages of the present invention will be more readily apparent from a review of the description of the preferred embodiment and the drawing and the claims which appear below.